Field of the Invention
The present invention relates to a mass spectrometry data processing apparatus and a mass spectrometry data processing method for use in two-dimensional mass spectrometry.
Description of Related Art
In two-dimensional mass spectrometry using a mass spectrometer, distribution information (mass imaging) of ions having a certain mass range can be obtained by analyzing a plurality of pieces of mass spectrometry data (i.e., mass spectra) each associated with position information of a corresponding position on a sample. The mass range is specified, for example, in the following manner. First, mass spectrometry is performed for individual micro areas within a certain two-dimensional range set on a sample to collect mass spectra. Then, an operator selects a substance of interest, that is, a mass range (see, for example, Japanese Patent No. 5206790).
In addition, the following method is disclosed as a data processing method for mass spectra in two-dimensional mass spectrometry. Specifically, a peak having the highest signal intensity, which is highly likely to indicate the most common substance, is searched for in a mass spectrum of each of micro areas. Then, the largest value is determined from among the retrieved highest signal intensities. A color scale for displaying the intensity is defined to correspond to a range from zero to the largest value. A display color corresponding to the highest signal intensity is determined for each micro area in accordance with the color scale. A colored two-dimensional image of the entirety or part of the two-dimensional range is created and displayed in a display window. Each micro area that contains a noticeable amount of substance is clearly shown in the colored two-dimensional image (mass spectrometric mapping image) regardless of the kind of peak, that is, the kind of substance in the mass spectrum of the micro area (see, Japanese Unexamined Patent Application Publication No. 2011-191222).
Because a mass spectrum is measured at many positions in two-dimensional mass spectrometry for mass imaging in order to improve the position resolution, measurement time taken for a mass spectrum (i.e., number of acquisitions) is limited. For this reason, each mass spectrum has a low signal-to-noise ratio (S/N). In addition, spike noise having a high peak intensity is sometimes detected. On the other hand, a peak corresponding to a locally present substance to be analyzed is sometimes not so high.
When no substance to be analyzed is specified, a mass range needs to be specified by selecting peaks to be focused on from among various peaks including spike noise in a vast number of mass spectra. Such a procedure is not only very laborious but also sometimes fails to find the mass range supposed to be analyzed.